Researchers from Northwestern University have developed a new class of ‘honeycomb’ gas separation materials to purify hydrogen rich mixtures like methane (natural gas) for generating electricity via fuel cells.

Traditional methods of gas separation use selective membranes that grab molecules by size. But Northwestern's Professor Mercouri G. Kanatzidis and Gerasimos S. Armatas are using a method of polarization. As the gas mixture of (carbon dioxide and hydrogen) travels through the inner walls of the ‘mesopourous’ membrane, the carbon dioxide (CO2) molecules are slowed down and pulled towards the wall as the hydrogen molecules pass through the holes.

One type of membrane consisting of heavy elements germanium, lead and tellurium showed to be approximately four times more selective at separating hydrogen than traditional methods using lighter elements such as silicon, oxygen and carbon. The process is reported to work at “convenient temperature range” -- between zero degrees Celsius and room temperature.

“We are taking advantage of what we call ‘soft’ atoms, which form the membrane’s walls,” said Kanatzidis. “These soft-wall atoms like to interact with other soft molecules passing by, slowing them down as they pass through the membrane. Hydrogen, the smallest element, is a ‘hard’ molecule. It zips right through while softer molecules, like carbon dioxide and methane take more time.”